Door knob



FIG. 1 is a front elevational view of the door knob showing my new design;

FIG. 2 is a side elevational view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is a rear elevational view thereof. 

The ornamental design for a door knob, as shown and described. 